I have a 7-year-old EB 4000 Honda generator, this fall it has surged. I started yesterday and needed choke to start, the auto choke wasn’t helping. I found that if I remove the air filter it would no longer surge or very little if any. I did connect a circular saw to test And found that it did not consistently stay at the same RPM and could tell that the saw speed was changing a very little not sure if this is normal.Can anyone give me any advice as to what to check next. I changed spark plug to ngk 6es as the parts manual says to use the 6es and the owners manual says to use the 5es.